The traditional method of administering therapeutic agents to treat diseases of the internal organs and vasculature has been by systemic delivery. Systemic delivery involves administering a therapeutic agent at a discrete location followed by the agent migrating throughout the patient's body including, of course, to the afflicted organ or area of the vasculature.
At the other end of the spectrum is local delivery, which comprises administering the therapeutic agent directly to the afflicted site. Localized delivery of therapeutic agents may be accomplished using implantable medical devices, e.g., drug-eluting stents (DESs). The efficacy of DESs is related to their ability to release drugs in a controlled manner.
One way this is accomplished is to include on the DES a rate-controlling layer, e.g., a topcoat layer, that is disposed over a drug reservoir layer and which comprises one or more polymers selected for their ability to mediate release of a particular drug or drugs from the underlying reservoir layer. These designs often provide slow release stents since drug release rate is impeded by the presence of the topcoat layer.
Another way to control drug release from a stent is by putting drugs in a drug reservoir layer that includes a polymeric matrix that mediates the release rate of the drug. Indeed, by manipulating the drug-to-polymer ratio, drug release can be controlled.
What is needed, however, are more tunable and accurate means for providing controlled drug release from a drug reservoir layer. The current invention provides such methods and addresses other deficiencies in the art.